Doesn't Ur-Priest have Iron Will as a prerequisite anyway?
Isn't Divine Orcale Skill Focus: Knowledge Religion?
Also; the first 5 levels are really a question of what do you want to do?
Are you going to be a pure caster? Than Wizard 3/Prestige Class 2 follows in that line, will give you some versatility (as will any of the weaker casters; beguiler, etc). You don't wnat Int based casting, so Sorcerer or Warmage could go here.
Are you going to mix in some melee? Than ToB stuff can't be beat. Barbarian 1 (Pounce)/Cloistered Cleric 1 (If your DM lets you keep domain abilities or devotion feats, this is still worth it, knowledge devotion, travel domain or travel devotion, law's devotion, luck domain, celerity domain)/fill with Warblade/Swordsage/Crusader as pleased
Do you want to do the skills thing? Rogue 2 gets you evasion. (So does monk 2; which will also provide some feats and a substantial save boost).
It's sorta unclear what you want to do.
I'm working on a guide to cleric prestige classes; here are some other filler ideas:
1) If you can get 1d6 of sneak attack in your first 5 levels, 3 levels of Shadowbane Stalker (CAdv) --- this works well for the skilled version
2) Church Inquisitor, mentioned; might have DM troubles (CDiv)
3) Radiant Servant of Pelor; will likely have DM troubles (CDiv)
4) Sacred Exorcist; hit die bump and minor abilities. (CDiv)
5) Ruathar; might have DM troubles (RotW)
6) Divine Disciple, might have DM troubles (PGtF)
7) Justiciar of Tyr (PGtF): Might have DM troubles